This invention relates to implantable medication devices and, in particular, to an implantable infusion device arranged to provide a flow of medication into the body. More particularly, this invention is directed to a component of such a device, a flow restrictor and/or regulator for purposes of providing a uniform, that is, constant flow right in the system despite varying external operating pressures.
Medication infusion devices are well known in the art such as the INFUSAID line of devices and a host patented technology as represented by U.S. Pat. Nos. 3,731,681, 4,511,355 and 4,626,244. Those three patents are representative of a host of technology which is directed to implantable devices which provide a relatively constant flow of medication from an implanted dispensing system. In these devices a flexible diaphragm or bellows defines a reservoir housing the medication. A relatively constant pressure is exerted on that diaphragm, for example, by utilizing freon or other vaporizable material to exert a pressure which is above body pressure. The medication is thus forced from the reservoir into a long capillary tube. The tube, by its length, is used as a flow limiting resistance. The medication is delivered to an infusion site at a point remote from the implantation site of the device.
In these fluid delivery systems a flow regulator may be used to provide a steady state output between the pump and the delivery site. Such devices may be accumulators, valved reservoirs and the like. There exists in the art a need to simplify such devices in implantable systems to improve reliability, reduce weight and bulk.
A standing requirement for such systems is compactness and reliability. Additionally, the materials which are used must be compatible with not only the medication which is employed, but also the in-vivo requirements.
Within the prior art various proposals have been made to decrease the size of certain components such as capillary systems utilizing silicon and micro machining concepts.
Reference is made to U.S. Pat. No. 4,537,680 which relates to an integral fluid filter and capillary wherein the capillary is formed by a groove that is etched in the surface of the silicon substrate. Silicon processing is done utilizing conventional semiconductor processing technology. A glass plate is bonded to the surface of the substrate to form a long capillary groove that has a very small cross-sectional area. Also utilizing silicon etching techniques, two comb filters are placed at each end of the capillary groove by defining a series of parallel grooves of smaller cross sectional area.
Reference is also made to U.S. Pat. No. 4,626,244 which describes an integral filter and capillary unit micromachined on a silicon substrate. The geometry of the filter and capillary unit is such that an inlet is positioned relative to a series of parallel filter grooves formed in the surface of the substrate. Medication from the inlet thus passes through the filter grooves and is collected in a series of channels of larger size. Those channels provide a supply of filtered medication to a capillary groove which is a series of reentrant loops formed on the silicon surface. The exit of the capillary channel comprises a series of parallel outlet filter grooves arranged about a central outlet collector area. The medication once passing through the outlet filter grooves to the outlet is supplied directly to the portion of the body under treatment by means of a capillary. Both the '680 and '244 patents thus define basic silicon micromachined comb and capillary systems.
Reference is made to "Normally Close Microvalve and Micropump Fabricated on a Silicon Wafer", M. Esashi et al, Proceedings of the IEEE Micro Electro Mechanical Systems, IEEE Catalog Number 89THO249-3 (1989) pp. 29-34". This article describes the fabrication of a microvalve and micropump on a silicon wafer by employing a silicon diaphragm and a piezoelectric actuator. The microvalve structure used for gas flow control comprises a valve structure mounted on a silicon substrate. An inlet is defined on the substrate with an outlet positioned by a pyrex glass cover. A piezoelectric actuator is employed to shift the silicon which has etched thereon a mesa surface which defines the valve.
While not prior art to this invention an article entitled, "Micromachined Silicon Microvalve", Ohnstein et al, IEEE Micro Electro Mechanical Systems (MEMS) 1990, IEEE Cat. No. 90 CH 2832-4 disclosed an electrostatically activated microvalve using silicon as a substrate having an orifice and a valve member made of a passivated silicon nitride. Electrodes are embedded in the structure to provide contacts for valve actuation. The valve acts as a bistable device between an open and a closed position or as a proportional flow control device as a function of applied voltage. Thus, the device operates as a valve requiring actuation for operation.
Despite such advances in the art of micromachined component structures utilizing silicon, a need still exists for components that have inhibited reducing the size of implantable devices. A reliable flow regulator-restrictor to be used with implantable systems that does not require exterior actuation and a power supply is one such requirement.